Feb. 3, 2011 -- The American Heart Association says in a new scientific statement that a rare and often underreported form of stroke involving the veins and not the arteries is more common than previously thought.

The AHA says the statement is its first on diagnosing and managing cerebral venous thrombosis, also known as CVT, which affects children, young adults, and women during pregnancy and in the postpartum period.

The statement is published in Stroke: Journal of the American Heart Association, and is a comprehensive review of diagnosing, imaging, and treating the disorder.

This type of stroke is caused by a clot in the dural venous sinuses, veins that drain blood from the brain toward the heart.

Facts About Cerebral Venous Thrombosis

According to the new statement:

Cerebral venous thrombosis disproportionately affects pregnant women or women taking oral contraceptives, as well as people 45 and younger.

The incidence of this type of stroke during pregnancy and postpartum periods ranges from one in 2,500 deliveries to one in 10,000 deliveries in Western countries. The greatest risk occurs during the third trimester and in the first four weeks of the postpartum period.

Oral contraceptive use increases risk of CVT. The statement authors, an international team of researchers, recommend that patients with suspected CVT undergo blood tests to determine if they have an inherited or acquired factor in the blood that predisposes them to blood clots.

Screening Recommended for Some Patients With CVT

The scientists also recommend screening patients for conditions that may predispose them to CVT, such as underlying inflammatory disease and infection or the use of oral contraceptives.

"A predisposing condition to form clots or a direct cause is identified in about two-thirds of patients with CVT," Gustavo Saposnik, MD, assistant professor of medicine at Saint Michael's Hospital at the University of Toronto, says in a news release. "Examples include pregnancy, immediate postpartum, dehydration or infections in children, and patients taking oral contraceptives. Some of these predisposing conditions are transient and reversible."

The statement says a blood test can determine whether a person has a hereditary condition that makes their blood more likely to clot and thereby increasing their risk of CVT.

The AHA statement says patients having a brain hemorrhage with an unclear cause should undergo an imaging scan of their cerebral veins. The most common symptom of CVT is headaches that progress in severity over days or weeks, and also seizures. Some patients may report double vision, weakness affecting their extremities, or other neurological findings.

CVT generally is diagnosed based on imaging and clinical suspicion. Magnetic resonance imaging is usually more sensitive to detecting CVT than CT imaging, the researchers say.

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SOURCES: News release, American Heart Association.Saposnik, G. Stroke: Journal of the American Heart Association, February 2011.